Many modern automotive and marine vehicles are equipped with an electronic control system for regulating various components of the vehicle. The system controls the components based on information represented by output signals from various sensors for detecting operating conditions. Accordingly, if the components or sensors malfunction, the vehicle's performance may be drastically affected and severe damage may result. However, because it is often difficult to distinguish a malfunctioning sensor from other vehicular problems, some type of sensor testing apparatus is necessary.
A number of devices for testing the performance of automotive electronic components have been developed, including both systems specifically directed toward vehicle control systems and testing devices aimed at vehicle electronic devices in general. U.S. Pat. Nos. 4,300,205 to Tansuwan, 4,447,801 to Masuda, 4,962,456 to Abe et al., and 5,235,527 to Ogawa et al. disclose devices specifically directed toward vehicle control systems and sensors.
Tansuwan '205 discloses a device for testing and calibrating a feedback and automatic idle speed control system for automobiles by simulating various operating characteristics of an automobile engine, and then monitoring the response of the control systems. The apparatus simulates the engine operating characteristics by generating output signals which mimic the expected output signals of various sensors. The output signals are transmitted to the control system and then the response of the system is compared to predetermined norms. A disadvantage of Tansuwan '205 is that the device disclosed therein does not test the performance of the vehicle sensors, but rather simulates them. Thus, the device may be useful for testing the control system as a whole, but it cannot diagnose problems with individual sensors. Another disadvantage of this prior art is that because the device simulates only an engine, problems not related to the engine, such as fluid level sensors and temperature sensors cannot be diagnosed.
Masuda '801 and Abe et al. '456 are both directed to systems that monitor a plurality of vehicle conditions and provide an indication of unsatisfactory operation. Masuda '801 discloses an on-board computer system which, upon ignition, tests various conditions using sensors. The sensors transmit electrical signals to a central processing unit (CPU), which determines whether the conditions are within expected ranges. If the sensed conditions are not within expected ranges, the CPU causes a warning light corresponding to the abnormal condition to light. Abe et al. '456 discloses a diagnosis device that interfaces with the control system for an automobile. The device reads electric signals from the vehicle's sensors and compares the signals with the data for the type of vehicle being tested. The type of vehicle must be entered into the device, which stores in computer memory data for various vehicles. The device notes any discrepancies between the stored signals and the actual signals to determine if the vehicle is operating properly.
A disadvantage of Masuda '801 and Abe et al. '456 is that, although both systems test the performance of various operating conditions generally, neither is capable of testing the operation of the sensors. Thus, a diagnosed malfunction may be created by some other component of the vehicle and not by a faulty sensor. Another disadvantage of these prior art systems is that both are computerized devices that contain CPUs and computer memory, making the devices expensive to manufacture. A further disadvantage of Masuda '801 is that the system therein disclosed is an on-board device, and therefore cannot be used to test multiple vehicles. A further disadvantage of Abe et al. '456 is that, because the device checks sensor output against data stored for various vehicles, new or uncommon vehicles for which data is not stored cannot be tested.
Ogawa et al. '527 discloses an on-board system for diagnosing an abnormal state of a sensor. The device converts the analog output of the sensor to a digital signal, forwards the signal to an electronic unit which recognizes the signal as a first value relating to a physical parameter by using data stored beforehand, stores that value relating to the physical parameter by using the stored data as an initial value, and then determines whether or not the parameter has changes by a predetermined value. If the parameter has changed by a predetermined value, the device converts a second analog output to a physical parameter, stores the second value, calculates the difference between the first and second values, and judges whether the difference is within an acceptable range.
A disadvantage of Ogawa et al. '527 is that, like Masuda '801, this diagnostic system is an on-board device, which can only be used to monitor a single vehicle. Another disadvantage of this prior art system is that the device requires an analog-to-digital converter, a CPU, read only memory (ROM), random access memory (RAM), and backup random access memory (B-RAM), thus making the complicated device expensive to manufacture. A further disadvantage of Ogawa et al. '527 is that to test a sensor, it must be installed in a functioning vehicle, making off-vehicle testing impossible.
U.S. Pat. Nos. 3,646,438 to Staff, 4,673,868 to Jones, Jr., and Re. 33,692 to Hirano et al. are directed to testing devices for vehicle electronic components in general.
Staff '438 and Jones, Jr. '868 disclose devices for testing the continuity of circuits employed in electrical components, such as switches, motors, relays, alternators, voltage regulators, and other similar components. With respect to Staff '438, current is passed through various components and the output is evaluated by examining a plurality of indicator lamps, a voltmeter, and an ammeter. By comparing the output of the component with an expected output, the operator can determine if the component is functioning properly. Regarding the Jones, Jr. '868 device, a pair of probes are contacted to two points on the component being tested to form a circuit. An indicator lamp and buzzer on the testing apparatus indicate if and how much current is flowing through the circuit. These indications are then compared to expected results, e.g., whether dim, bright, or no illumination, or whether a soft, loud, or no buzzing, is expected for the particular contact points on the component.
A disadvantage of Staff '438 and Jones, Jr. '868 is that the prior art devices disclosed therein may only be used to test electrical components containing simple circuits. These testing devices may not be able to diagnose malfunctioning sensors because modern sensors contain circuitry more advanced than the electronic components for which the prior art inventions were designed. Another disadvantage of both prior art devices is that the method of determining the results of the test, which requires the operator to compare the output to a chart or list of the expected output, is complicated and time-intensive. Moreover, the operator may lose the chart of expected outcomes, making the testing device useless, or may misread the chart of expected outcomes, corrupting the test.
Hirano et al. '692 discloses a fault diagnosis system for displaying malfunctions detected in automobile electronic devices. The electronic devices output fault diagnoses according to one of a plurality of output signal schemes and also a signal that identifies which scheme the device is outputting. The testing system receives the fault diagnoses and translates the information according to the signal scheme identifier so that any malfunctions may be displayed. A disadvantage of this prior art system is that each individual electronic device must output a fault diagnosis signal. The sensors currently in use do not do this, and thus would not be compatible with the Hirano et al. '692 system. A further disadvantage of this fault diagnosis system is that the device displays only faults affecting whole electronic devices, and not component parts, such as sensors. As such, the testing apparatus cannot pinpoint a fault as being caused by a sensor as opposed to some other component of the electronic device as a whole.
A disadvantage of all of the aforementioned devices is that none of them are capable of testing the functionality of vehicle knock sensors. Neither are the above devices capable of testing the proper functioning of vehicle speed sensors or ignition coils.
What is desired, therefore, is a sensor tester which is capable of testing a plurality of sensor types, including vehicle knock sensors, vehicle speed sensors and ignition coils, which can test individual sensors and not just vehicle components, which can test existing sensors without requiring sensor modification, which can test sensors from multiple vehicles, which can test sensors off-vehicle before they are installed, and which does not require the use of a CPU or computer memory.